Let's review. Monosaccharides are the simplest unit of carbohydrates. They're composed of carbon, hydrogen, and oxygen atoms, and they cannot be broken down further since they are already in their simplest form. Their general formula is (CH2O) n , where n is any number equal or greater than 3. If n = 3, then there are three carbon atoms, so these monosaccharide units are called trioses. If n = 4, there are four carbon atoms, and these are called tetroses, and if n = 5, the monosaccharides are classified as pentoses.